Group II-VI compound semiconductor particles comprising compounds of Group II and VI elements, e.g., semiconductor particles mainly containing zinc sulfide and the like, have properties that, when an activating element (activator) such as manganese, copper, silver, terbium, thulium, europium, and fluorine is added, the particles absorb energy of light, electron beams and the like to emit light. Thus, fluorescent bodies obtained using semiconductor particles mainly containing zinc sulfide and the like, as fluorescent body bases are used in displays such as plasma displays, electroluminescent displays, and field-emission displays.
Known methods for obtaining fluorescent body precursors using semiconductor particles mainly containing zinc sulfide and the like, as fluorescent body bases include a method comprising primary firing carried out at a very high temperature of 800° C. to 1300° C. on zinc sulfide particles, which are raw materials, together with an inorganic salt called a flux to cause the particles to grow to form micron-size particles, and secondary firing carried out at 500° C. to 1000° C. to obtain fluorescent body precursors (refer to Patent Documents 1 to 3). This method, however, uses heat to exchange ions. Thus, it is difficult to preferentially introduce a metallic element having a larger ionic radius than those of metallic elements constituting Group II-VI compound semiconductors, making it extremely difficult to obtain zinc sulfide fluorescent body particles with higher brightness.
In cases of synthesizing a Group II-VI fluorescent body precursor in a liquid phase, an activator or a co-activator can be added during particle growth, and an amount of the activator or the co-activator to be added can be controlled. This makes it possible to prepare fluorescent body particles with a homogenized concentration distribution of the activator or the co-activator in the particles. Further, monodispersed particles with a narrow particle size distribution can be obtained if nucleation and growth are separated to form the particles, and if a degree of supersaturation during the growth of particles is controlled.
Synthesizing particles under hydrothermal conditions (refer to, for instance, Patent Document 4) is a known-method for synthesizing a Group II-VI fluorescent body precursor in a liquid phase. Further, methods for controlling particle size distributions are disclosed as modified methods for adjusting liquid phases (refer to, for instance, Patent Document 5). However, although a liquid phase reaction produces an effect that cannot be obtained by a firing method, since the liquid phase reaction utilizes template effect of chelates, it is difficult to preferentially introduce a metallic element having a larger ionic radius than those of metallic elements constituting Group II-VI compound semiconductors. Thus, it is difficult to obtain zinc sulfide fluorescent body particles with higher brightness by the liquid phase reaction.
Further, application of pressure on fluorescent body precursors using an autoclave, a mechanical presser or the like, and wet ball milling of fluorescent body precursors are proposed as methods for improving luminescent performance of fluorescent bodies, and preparation of fluorescent bodies by an explosion method is also proposed (refer to, for instance, Patent Documents 6 and 7, and Non-patent Document 1).
[Patent Document 1]
Japanese Unexamined Patent Publication No. 183954/1996 (Tokukaihei 8-183954)
[Patent Document 2]
Japanese Unexamined Patent Publication No. 62342/1995 (Tokukaihei 7-62342)
[Patent Document 3]
Japanese Unexamined Patent Publication No. 330035/1994 (Tokukaihei 6-330035)
[Patent Document 4]
Japanese Unexamined Patent Publication No. 306713/2005 (Tokukai 2005-306713)
[Patent Document 5]
Japanese Unexamined Patent Publication No. 139372/2005 (Tokukai 2005-139372)
[Patent Document 6]
Japanese Unexamined Patent Publication No. 281451/2005 (Tokukai 2005-281451)
[Patent Document 7]
Japanese Unexamined Patent Publication No. 336587/1994 (Tokukaihei 6-336587)
[Non-patent Document 1]
Xiaojie Li et al, “Preparation of SrAl2O4: Eu2+, Dy3+ nanometer phosphors by detonation method” (2006) Materials Letters p. 3673-3677.